I am using 4 2 cell 5000mAh 60C LiPo's in series to drive a robot I am building for Robot Wars (Scorpinator - look out for it). Each battery came with a balance cable built into the discharge cables but one of my chargers is capable of charging 8S Lipos (which when connected together these are) so I want to try and charge all batteries together to save time but connected together I end up with an 8S with 4x 2S balance cables - no good.

I have searched all over to see what a 8S balance cable should like e.g. which cables connect to which pins, I have found numerous diagrams but none of them specifically show 4x 2S to single balance cable (I found examples of a single 8S battery and 2x 4S). If and when I get the balance cable sorted should I charge in series or parallel? Is there a formula that explains the why and how of balance cables that can be used for any LiPo configuration rather than having to keep a library of different configs? Ideally I want to understand how the cables connect rather than just find a cable gadget that connects 4x 3pin balance cables to a 9 pin (not that I could find one anyway - I tried!)

2 Answers
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If you haven't figured this out yet, series charging is accomplished by putting all the main power leads in series, and then putting the balance leads in series as well. The challenge is that each balance lead has an extra pin from the number of cells -- that's where the confusion comes in.

The first and last pins of the balance leads are directly connected to the first and last cells respectively, positive and ground. Think logically about how a fully-series pack is constructed, and where the balance taps are. They are between the positive and negative of each cell in series. Since your balance leads are broken out, you have one wire for a positive, and another wire for a negative.

\$\begingroup\$You can use a voltmeter to figure out which balance leads go where in the stack, if there's any confusion. Connect the positive main power lead of battery A to the negative main power lead of battery B. Now connect one end of your voltmeter to the negative main power lead of A, and use the other end to probe the balance leads of battery A. You should see a series of voltages differing by the one-cell voltage, with the final balance lead reading the voltage of the whole pack. Now, the first balance lead on the second pack should show the SAME voltage -- those two same-voltage leads go together.\$\endgroup\$
– Glenn WillenJun 23 '18 at 21:34

\$\begingroup\$... gosh, this question and answer are ancient, I'm not sure why it showed up as trending. I will leave my comment anyway, in case it's helpful to anybody else. :-)\$\endgroup\$
– Glenn WillenJun 23 '18 at 21:35

Let us take a lipo battery with 8 cells in series. Then the charger requires a connection to the two end poles and all individual cells. That makes 9 wires in the balancer cable. If you have 2 identical ( same capacity, same manufacturer, same age) batteries packs then you can connect them in series and hook them up to the balancer as if it was one battery pack.

If you have a 4S2P pack than that means 4 cells in series and 4 times 2 cells in parallel. Such a pack has a connector with 5 wires for the balancer.
Now if we put 2 such packs in series then we end up with 10 wires. For the balancer you need only 9. The series connection gives you 2 wires combined. For the balancer you need only one of them. You end up with a system 8S2P.

\$\begingroup\$Thanks for your feedback Decapod but your explanation does not actually tell me which wires go to which pins. BTW my set up is 2S1P times 4 amazon.co.uk/gp/product/B00SKFEZH6/…\$\endgroup\$
– Lee WilsonOct 20 '16 at 15:08

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\$\begingroup\$Please make a schematic of your 2S1P including the balancing wires and show put that in your question. Number the balancing wires and make a suggestion of wat to connect together. If you then run into a problem we can continue. Mistakes should not be made. So you have to understand what you are doing.\$\endgroup\$
– DecapodOct 21 '16 at 10:02